{ "schema_version": 2, "id": "commands/cf.reserve", "title": "CF.RESERVE", "url": "https://redis.io/docs/latest/commands/cf.reserve/", "summary": "Creates a new Cuckoo Filter", "since": "1.0.0", "tags": [ "docs", "develop", "stack", "oss", "rs", "rc", "oss", "kubernetes", "clients" ], "last_updated": "2026-09-18T09:48:54+01:00", "page_type": "content", "content_hash": "eb2e11d669f27947e55e6e8aa37d0c2b056d34920b7765d3eeb06ce3906f466c", "sections": [ { "id": "overview", "title": "Overview", "role": "overview", "text": "Creates an empty cuckoo filter with a single sub-filter for the initial specified capacity.\n\nAccording to the cuckoo filter behavior, the filter is likely to declare itself full before `capacity` is reached; therefore, the fill rate will likely never reach 100 percent.\nThe fill rate can be improved by using a larger `bucketsize` at the cost of a higher error rate.\nWhen the filter self-declare itself `full`, it will auto-expand by generating additional sub-filters at the cost of reduced performance and increased error rate.\nThe new sub-filter is created with size of the previous sub-filter multiplied by `expansion`.\nLike bucket size, additional sub-filters grow the error rate linearly.\n\nThe minimal false positive error rate is 2/255 ≈ 0.78% when bucket size of 1 is used.\nLarger buckets increase the error rate linearly (for example, a bucket size of 3 yields a 2.35% error rate) but improve the fill rate of the filter.\n\n`maxiterations` dictates the number of attempts to find a slot for the incoming fingerprint.\nOnce the filter gets full, high `maxIterations` value will slow down insertions.\n\nUnused capacity in prior sub-filters is automatically used when possible. \nThe filter can grow up to 32 times." }, { "id": "required-arguments", "title": "Required arguments", "role": "content", "text": "
key\n\nis key name for the cuckoo filter to be created.\n
\n\n
capacity\n\nEstimated capacity for the filter.\n\nCapacity is rounded to the next `2^n` number.\n\nThe filter will likely not fill up to 100% of it's capacity. Make sure to reserve extra capacity if you want to avoid expansions.\n
" }, { "id": "optional-arguments", "title": "Optional arguments", "role": "parameters", "text": "
BUCKETSIZE bucketsize\n\nNumber of items in each bucket.\n\nA higher bucket size value improves the fill rate but also causes a higher error rate and slightly slower performance.\n\n`bucketsize` is an integer between 1 and 255. The default value is 2.\n
\n\n
MAXITERATIONS maxiterations\n\nNumber of attempts to swap items between buckets before declaring filter as full and creating an additional filter. \n\nA low value is better for performance and a higher number is better for filter fill rate.\n\n`maxiterations` is an integer between 1 and 65535. The default value is 20.\n
\n\n
EXPANSION expansion\n\nWhen a new filter is created, its size is the size of the current filter multiplied by `expansion`.\n\n`expansion` is an integer between 0 and 32768. The default value is 1.\n\nExpansion is rounded to the next `2^n` number. \n
" }, { "id": "examples", "title": "Examples", "role": "example", "text": "redis> CF.RESERVE cf 1000\nOK\n\nredis> CF.RESERVE cf 1000\n(error) ERR item exists\n\nredis> CF.RESERVE cf_params 1000 BUCKETSIZE 8 MAXITERATIONS 20 EXPANSION 2\nOK" }, { "id": "redis-software-and-redis-cloud-compatibility", "title": "Redis Software and Redis Cloud compatibility", "role": "content", "text": "| Redis
Software | Redis
Cloud | Notes |\n|:----------------------|:-----------------|:------|\n| ✅ Supported
| ✅ Flexible & Annual
✅ Free & Fixed | |" }, { "id": "return-information", "title": "Return information", "role": "returns", "text": "**RESP2:**\n\nOne of the following:\n* [Simple string reply](https://redis.io/docs/latest/develop/reference/protocol-spec#simple-strings): `OK` if the filter was created successfully.\n* [Simple error reply](https://redis.io/docs/latest/develop/reference/protocol-spec#simple-errors) in these cases: invalid arguments or the key already exists.\n\n**RESP3:**\n\nOne of the following:\n* [Simple string reply](https://redis.io/docs/latest/develop/reference/protocol-spec#simple-strings): `OK` if the filter was created successfully.\n* [Simple error reply](https://redis.io/docs/latest/develop/reference/protocol-spec#simple-errors) in these cases: invalid arguments or the key already exists." } ], "examples": [] }